Wireline formation testing data are essential for analyzing and improving reservoir performance and making reliable predictions, and for optimizing reservoir development and management.
Knowing the ratio of the relative permeability of formation fluids may allow for more accurate prediction of oil displacement by water and therefore of reservoir production.
Wettability is also a very important parameter in reservoir engineering as it is needed for accurate production predictions. Wettability exerts a profound influence on the displacement of oil by water from oil producing fields. Therefore, accurate predictions on the development of oil and gas reservoirs depend on the wettability assumptions. In particular, during early production of a reservoir, such as during the exploration well and/or appraisal well stages, characterizing wettability is one important parameter that is used in reservoir engineering.
Measuring a certain wettability index in-situ with the available techniques is challenging. Specifically, it is generally very difficult to characterize or qualify formation wettability, so wettability is measured indirectly through other reservoir properties that affect wettability, such as relative permeability, capillary pressure, or water saturation profile in the transition zone.
Elshahawi et al., Capillary Pressure and Rock Wettability Effects on Wireline Formation Tester Measurements, SPE 56712, have described a way to measure capillary pressure in-situ, from which an assumption on the formation wettability can be made.
Freedman et al., Wettability, Saturation, and Viscosity from NMR Measurements, SPE Journal, December 2003 or Looyestijin et al., Wettability Index Determination by Nuclear Magnetic Resonance, SPE 93624 have also developed a theory to deduce a wettability index from NMR transverse relaxation time T2, but to the inventors' knowledge it has not been tried in-situ to this time.
U.S. Pat. No. 7,032,661 B2 describes a method and apparatus for combined NMR and formation testing for assessing relative permeability with formation testing and nuclear magnetic resonance testing.